WOOD MATERIALS TECHNOLOGY

4th Edition

Chapter 29Finishes

Protects the wood from wear and tear

Prevents decay – fungus, insectsProvides a nice finished surfaceEnhances colourChanges the colour (staining)

Purpose of a finish

Surface preparation– Getting the surfaces smooth and

clean– Preparing the piece before

putting on the finish

Applying the finish– The steps in putting on the

different layers of chosen finish– Different finishes will have

slightly different steps

Surface preparation

Application of finish

Finishing stages

Rub out/remove pencil lines Scratches and marks can be removed

using a scraper Punch nails and pins Fill nail holes and small cracks using a

suitable wood filler Sand the surfaces smooth using

sandpaper Sand end grain Start with 100 grit (medium)

sandpaper, then with 180 grit and finally 320 grit (very fine)

Always sand with the grain – avoid scratching the surface

Brush off all dust or use a tack cloth

Surface finish

Sandpaper (glass paper)

Composition of sandpaper– Grit is bonded to the

backing paper or card– The grit size is printed on

the back of the sandpaper

Types of abrasive

Always sand with the grain

Always sand end grain

Sanding

Advantages– Good inside and outside– Lots of colours available– Durable– Long-lasting– Easily-cleaned– Covers scratches and

defects well

Disadvantages– Hides the beauty of the

wood– Difficult to apply well– Needs good preparation– Can blister and peel

Paint

Prepare surfaces wellSeal knots with knottingApply primer to all surfacesFill cracks and holesApply 1 – 2 coats of

undercoat Sand lightlyApply final finish coatAllow each coat to dry fully

Painting wood

Why choose varnish?– Water-resistant – Scratch-resistant– Easily-cleaned – Clear finish enhances

the grain of the wood– Resists heat – Stains/coloured varnish

are available

Varnish

Apply the varnish with a brush/cloth, working with the grain

Cover all surfaces evenly, with no drips/runs

When the first coat is applied, allow to dry

Sand lightly between coats (denib) with very fine sandpaper or fine wire wool

Apply another coat of varnish evenly and leave to dry again

Repeat the process until you have three coats applied

Varnish – application

Microporous finishes

Breathable skinProtect the wood from the

weatherAllow moisture to evaporate

from the woodDo not flake or blisterEnvironmentally friendlyFor external use, e.g.

sheds/fences

Danish oil

Why choose Danish oil?– Easy to apply– Doesn't raise the grain– Gives a nice shine– Wood can be re-oiled– Suitable for outdoor use

Danish oil – application

Apply with a cloth, work oil well into the grain

Apply two or three coats and leave to dry overnight

De-nib any rough surfaces using light sandpaper

Apply another three coats of oilGradually build up the finish using

the above process

Wax finishes

Why choose wax?– Easy to apply– Does not raise the grain– Gives nice lustre/shine– Easy to renew– Allows polish to be built

up – No sanding between coats– Indoor use only

Wax finishes – application After surface finishing, seal the

wood with a wood sealer Using a clean dry cloth apply the

wax rubbing well into the wood Build up a number of coats before

letting the wax dry for a while Polish the surface to bring up a

shine Repeat the process to build up to a

high gloss shine Wax is a soft finish and is not water-

resistant, so it can only be used indoors

Lacquer

Applied by spraying Special equipment is

requiredProper extraction

system is requiredLacquer is harmful if

inhaled

Spray gun

Quiz

• Seals the wood • Prevents dirt getting in• Enhances the appearance

of the piece• Protects the wood from

wear and tear

Why is it necessary to apply a finish to a wooden artefact?

− White spirit

What is used to clean a brush after applying oil-based paint or varnish?

− Rub out/remove pencil lines− Scratches and marks can be removed using a scraper− Punch nails and pins − Fill nail holes and small cracks using a suitable wood filler− Sand the surfaces smooth using sandpaper− Sand end grain − Start with 100 grit (medium) sandpaper, then with 180 grit and finally 320 grit (very

fine)− Always sand with the grain – avoid scratching the surface− Brush off all dust or use a tack cloth

List the steps required to prepare a wooden item for an applied finish

• Microporous varnish, e.g. Fencelife− Protects the wood− Makes the wood look good− Allows the wood to breathe− Easy to apply− Prevents decay− Does not blister or flake

Suggest a finish suitable for a picnic table and give reasons for your choice

− Prepare the surface very well − Apply varnish to the surfaces with a brush

or cloth, work with the grain− Cover all surfaces evenly with no

drips/runs− When the first coat is applied, allow to dry− Sand lightly between coats with very fine

sandpaper or fine wire wool− Apply another coat of varnish evenly and

leave to dry again− Repeat the process until you have three

coats applied

Describe the steps in applying varnish to the unit shown